Contemporary fluid dispense systems are well suited for dispensing precise amounts of fluid at precise positions on a substrate. A pump transports the fluid to a dispense tip, also referred to as a “pin” or “needle”, which is positioned over the substrate by a micropositioner, thereby providing patterns of fluid on the substrate as needed. As an example application, fluid delivery systems can be utilized for depositing precise volumes of adhesives, for example, glue, resin, or paste, during a circuit board assembly process, in the form of dots for high-speed applications, or in the form of lines for providing underfill or encapsulation.
Contemporary dispensing pumps comprise a syringe, a feed tube, a dispense cartridge, and a pump drive mechanism. The syringe contains fluid for dispensing, and has an opening at its distal end at which a feed tube is connected. The feed tube is a flexible, or rigid, hollow tube for delivering the fluid to the cartridge. The cartridge is hollow and cylindrical and includes an inlet neck at which the opposite end of the feed tube is connected. The inlet neck directs the fluid into the hollow, central cartridge chamber.
A feed screw disposed longitudinally through the center of the cylindrical chamber transports the fluid in Archimedes principle fashion from the inlet to a dispensing needle attached to the chamber outlet. A motor drives the feed screw via a rotary clutch, which is selectively actuated to engage the feed screw and thereby effect dispensing. Alternatively, a closed loop servomotor may be employed for providing precise control over the angular position, velocity and acceleration of the rotation of the feed screw during a dispensing operation, as described in U.S. Pat. No. 6,511,301, incorporated herein by reference above. A bellows linkage between the motor and cartridge allows for flexibility in system alignment.
Pump systems can be characterized generally as “fixed-z” or “floating-z” (floating-z is also referred to as “compliant-z”). Fixed-z systems are adapted for applications that do not require contact between the dispense tip and the substrate during dispensing. In fixed-z applications, the dispense tip is positioned and suspended above the substrate by a predetermined distance, and the fluid is dropped onto the substrate from above. In floating-z applications, the tip is provided with a standoff, or “foot”, designed to contact the substrate as fluid is delivered by the pump through the tip. Such floating-z systems allow for tip travel, relative to the pump body, such that the entire weight of the pump does not bear down on the substrate.
In certain applications, the material being dispensed is heated in order to lessen its viscosity. Heating of the material also allows for improved control over process temperature, for example in environments where ambient temperature can vary greatly over the course of a day, or over the course of a year.
The heating of material flow has been accomplished in a number of ways. In one approach, a heated reservoir is placed in line with the feed tube such that the material enters the pump already heated. However, this approach leads to a more complicated configuration that is difficult to clean.
In another approach, hot air is generated and circulated down the fluid path. However, this approach is mechanically complex, and involves the movement of air above components, which can affect the reliability of the dispensing operation.
In another approach, resistive heaters are formed in the shape of cylindrical cartridges that are mounted to the pump body. In such heaters, referred to in the industry as “cartridge” heaters, a cylindrical metal jacket encases a resistive winding. In these embodiments, the heat tends to be localized to the region of the cylinder. In addition, due to the tolerances of the cylinder, air gaps can form between the inner circumference of the cylinder and the body of the pump, leading to inaccurate and inefficient heating.